On Sat, 09 Feb 2008 17:16:07 -0600, Bruce W. Ellis
wrote:

I am considering a horizontal loop antenna that would be "squarish"
(depending on tree locations) and about 400' in circumference. My
(automatic) tuner is located in my garage (with 100' of coax going to
the shack in the house). The lead wires for the antenna and ground
are short and direct through the garage wall - I don't envision any
feedline from tuner to the wire loop. I don't want to use a balun
since there isn't really any feedline to balance and the impedances
presented to the balun would be all over the (Smith) chart.

Hi Bruce,

Well, in fact you have described a feedline - the one going to the
automatic tuner. This one has every need for choking as any line that
left the tuner (which is, by and large, not recommended by most
automatic tuner vendors). You probably also have DC power or control
lines going to that tuner as well. They need choking too.

However, given you also mention a 100 run, then this presumably means
along or under ground. Ground proximity would probably snub any
Common Mode currents which would then reduce your specific need for
choking.

Would it
make sense to feed one end of the loop from the tuner and connect the
other loop end to the ground connection near the tuner or just leave
it open (essentially a square longwire antenna)?

You might want to make it switchable.

I would also have
three counterpoise wires following the loop lying on the surface of
the ground.

This technique falls outside of the canon of most lore, but not
without its benefits. However, three wires will not provide much
efficiency gain. On the plus side, it could make a difference for
NVIS.

You don't mention much about frequencies of operation nor about
directionality.

The articles that I can find all use openwire feedlines
and balanced tuners (or baluns) but that arrangement doesn't fit my
situation. Thanks W0BF

You have enough to work with as it is. As for openwire or coax
feedlines; to my knowledge, autotuners are built to feed unbalanced
antennas directly (at the feedpoint) rather than as traditional hand
adjusted tuners being used away from the antenna. This is, perhaps, a
bias from seeing too many SGCs. Anyway, I don't see a downside to
your plan.

73's
Richard Clark, KB7QHC